Field of the Invention
The present invention relates to a lithium secondary battery, and more specifically, to a lithium secondary battery with excellent high-temperature storage and life-span properties.
Description of Related Art
With rapid progress of electronic, telecommunication and computer industries, portable electronic communication devices such as a camcorder, mobile phone, notebook PC, etc. have been remarkably developed. Accordingly, the demand for a lithium secondary battery as a power source capable of driving the above device is also increased. In particular, with regard to applications of eco-friendly power sources such as an electric car, uninterruptible power supply, electromotive tool and satellite, research and development have been actively proceeded in domestic field and other countries such as Japan, Europe, United States, etc.
Among currently used secondary batteries, the lithium secondary battery developed since early 1990's includes a cathode made of a carbon material capable of absorbing and desorbing lithium ions, an anode made of lithium-containing oxide, and a non-aqueous electrolyte containing lithium salt dissolved in a mixed organic solvent in a suitable amount.
In this regard, as the application of the lithium secondary battery is more enlarged, a case that the lithium secondary battery should be used even under more severe environments is increased.
However, lithium transition metal oxide or composite oxide used as a cathode active material of the lithium secondary battery entails a problem that a metal component is desorbed from the cathode during storage at a high temperature under fully charged condition, hence being in thermally unstable state.
In addition, when using a high-capacity cathode active material for a secondary battery with high energy density, the battery capacity may be increased, but life-span and high-temperature storage properties are decreased. Therefore, in order to prevent this phenomenon, a technique of using artificial graphite together with the cathode active material for the anode has been developed, there is still such a problem that an improvement width of the life-span and high-temperature storage properties is not large.
In order to solve the above problem, Korean Patent Laid-Open Publication No. 2006-0134631 discloses a cathode active material of core-shell structure having a core part and a shell part which are made of lithium transition metal oxides different from each other, however, still has lack of improvement in life-span and high-temperature storage properties.